Nipah virus (NiV) and Hendra virus (HeV) are closely related viral zoonoses that form the genus Henipavirus in the family Paramyxoviridae. They are enveloped, negative-sense RNA viruses that cause a systemic and fatal disease in a variety of animal hosts and in humans. In some outbreaks, the death toll has reached as high as 75%. They are classified as biological safety level-4 (BSL4) viruses and possess several characteristics that justify their listing as Category C biothreat agents by the NIH and CDC including the ability to be transmitted via aerosol. There is currently no approved vaccine or therapeutic against either NiV or HeV. Annual outbreaks of NiV human infections in Bangladesh and other areas justify the benefit of a prophylactic vaccine for improving public health as well as reducing their potential as a biothreat. Immunization and challenge studies performed in cats, ferrets, and nonhuman primates using recombinant HeV soluble attachment protein G, HeV-sG, have demonstrated that a HeV-sG subunit vaccine can be completely effective against both HeV and NiV. In fact, HeV-sG subunit is currently being evaluated in Australia as an equine vaccine. Our objective here is to produce 1 gram of HeV-sG that will be suitable to perform IND-supportive toxicology and efficacy studies as necessary steps to support the evaluation of HeV-sG as a human vaccine against NiV and HeV. We will do so through the following specific aims: 1) Optimize HeV-sG immunogen/adjuvant formulation; 2) Identify release assays for HeV-sG; 3) Manufacture 1 g of HeV-sG; 4) Perform IND supportive animal studies. By the end of the funding period, we will have (i) identified an adjuvant suitable for further clinical development; ii) prepared a characterized research-grade pre-seed for use to manufacture a HeV-sG Master Cell Bank; (iii) optimized a development-scale process suitable for the manufacturing of cGMP clinical trial materials under future proposals; (iv) manufactured at least 1 g of development-grade vaccine to perform IND supportive toxicology and efficacy studies, and (v) executed said animal studies. Subsequent applications will pursue cGMP manufacture of 1) a master cell bank and 2) clinical lots of HeV-sG vaccine for Phase 1 clinical evaluation.